As a London commuter (go past the Shard twice a day as it happens) I really struggle with this 300 in 2 hours. Given that all our reports basically speak to the same thing - carts in busy areas but little to zero actual engagement - its improbable.
I also used to see the carts outside Charing Cross Station at peak times, but these have disappeared in the last few months. The JW's there were competing with the following:
City AM
Time Out
Gym Membership freebies
Free product trial offers - meal replacement bars etc
The homeless guy selling Big Issue
The homeless guy who has wet himself (again)
Actual real charities - Breast Cancer day etc...
I wouldn't be surprised if Westminster Council told the JW's to sling their hook as it was becoming a road traffic safety issue with thousands of commuters fighting their way through all the 'offers' to cross one of the busiest roads in central London.